Two-stroke cycle internal combustion engine



June 24, 1930. J. w. RoBERTsoN 1,767,402

TWO-STROKE CYCLE INTERNAL COMBQSTION ENGINE Filed Aug. 2v, 1929 m Mw@ (RM fio Patented June 24, 1930 UNITED; vSTATES T'ENToFfFicE JAMES WALTER BoBEn'rsoN,`oE DEYMEN, SCOTLAND Two-STROKE CYCLE IiwrEraivnL` coMBUsTIoNENGI-NE Appucation'mea August 27, 1929, serial No. 388,63?, ami in Great ieritainseptemter 5, 192s, `y

This invention relates to two-stroke cycle Vinternal combustion engines.

In the operation of the normal type of two-stroke cycle internal Vcombustion engine in which transfer is effected at atmospheric pressure it is only possible to admit comparatively small weight of charge without incurring Vserious lloss of fuel through the exhaust ports. The scavenging of such an engine is imperfect; the provision of a deliector piston is objectionable; and the remcteness of the spark plug f om the transfer ports prevents even firing at low speeds.

In two-stroke cycle engines of the type having an air scavenge and subsequent transfer at atmospheric pressure, some only of these defects are overcome. 'Y l The type in which the transfer of the charge is effected after the exhaust ports are closed Vis the most promising, but in this type it is necessary to effect at least a partial scavenge while the exhaust ports are open. To effect this scavenge by means of air alone is diflicultv without undue com-- plication and not wholly desirable.`

The invention has for its primary object to provide an arrano'ement whereby a small measured volume of fresh mixture may be used to effect partiall scavenge while the exhaust parts are open, followed by transfer at super-atmospheric pressure after the exhaust ports areclosed.

In the drawing Fig. 1 is a vertical transversel section of a two-stroke cycle internal combustion engine according to the invention; Fig. 2 is a diagram showing the cycle of operations. l n

Referring to the drawing, 1 Adenotes the upper barrel and 2 the lower barrel (of a two-diameter cylinder formed with transfer passages 3 and fitted with a two-diameter sleeve l in which works a piston. 5 having a flared skirt 6 adapted to operate in the enlarged lower end 4L Vof the sleeve el. VThe sleeve and piston reciprocate within the cylinder with the same frequency but out of phase. rl`he trunk ofthe piston is luted at 7. l

The annular space 8 formed between the piston skirtA and the sleeve constitutes a compressor cylinder which at a predetermined `period during each cycle communi- Cates.` with the cylinderproper by way of the transfer passages 3 and ports -9, 10 formed, respectively, ynear vthe upper end and near the lower end of the top portion l ofthe sleeve and oo-operating, in the operation of the engine, with the upper and lower ends of the'tr'ansfer passages. 11 denotes exhaust ports formedin the sleeve intermediate-theports 9, 10,'and coacting, iu

the operationof the engine, lwith exhaust ports 12. formed in the `cylinder wall intermediate the upper and lower-'ends of the' transfer passagesr 3. Thev lower` cylinder barrel 12 is :provided with an inductioninlet passage 18; adapted-to communicate witl'i `the compressor cylinderS under the control of inlet ports ,14 formed in the enlarged lower end 4 -Of the sleeve.V l5y denotes theicylinder head-fitted with a spark plug 16,1andserfing tosealthefupper end ofthe sleeve. The

combustion space 17 is suitablyr shapedto accumulate fresh charge at the spark plug pointstofensure even firing Vat ylow speeds,

the upper en ds of the transferpassage 3 b ex ing 4inclined to the-cylinder axis. ,i The annular space 18 between .the sleeve and the cylinder is vented at .19 tothe crankcase.20.fv A i l Referringl to the `diagram shown in Fig. 2, a cyclelof operation is as follows In the ascent of the piston from the bottom dead-centre B, the'direction of rotation being indicated bythe arrow A,;the exhaust ports 11 of the sleeve 1, which are still partially in register with the exhaust. ports 12fof the-cylinder, are closed at the point C by the top of the piston 5 and thejlower transfer-ports 10ofthev sleeve which are 9 V,Transfer continues until, at the point M,

minimum volume is attained in the compressor. At the point M the sleeve closes both ends of the transfer passages 3,. thus trapping a Ineasuredvolume of highly com- 5 pressed charge in the transfer passages. The piston travels slightly upwards towards top dead-centre T and ignition takes place, the upper transfer ports t 9 in the sleeve being sealed by the junk head'l and the ie sleeve exhaust ports 11 in the piston.v The cylinder exhaust' ports 1-2 are only fully closed by the sleeve by the time the piston is at the first stage -of rits descent. The sleeve exhaust ports 11 are uncovered by the l5 piston and the cylinder exhaust ports 12 are then uncovered by the sleeve exhaust ports 11 at the point O. The sleeve inlet ports 14 are registering with the induction passage 13, having themselves been uncovered by the 2G skirt of the piston in its downward travel, the opening to induction occurring as soon as the pressure in the compressor cylinder 8 has dropped to atmospheric. Induction takes place over the angle y. The exhaust ports 11, 12 .are still open,` exhaust taking place over the angle Thet transfer ports 9, 10 are uncovering the ends of the transfer passages, the ports 10, however, being sealed by the piston. A measured volume of charge previously Acontained in the transfer passages 3 thus enters the cylinder at a point remote from the exhaust ports and effects a partial scavenge. Scavenge is effected over the angle up to the point C. The induction passage 13 is sealed by the sleeve, the kexhaust ports 11, 12 are closed as before and the main charge is about to be compressed.

I claim.: A two-stroke cycle internal combustion engine comprising, in combination, a twodiameter cylinder provided with transfer passages, exhaust ports intermediate the v upper and lower ends of said passages, and 4 an inlet in the part of larger diameter, a vtwo-diameter ported sleeve reciprocable in said cylinder, a piston having a fluted vtrunk and an enlarged skirt and reciprocable in said sleeve, said sleeve and said piston being adapted to reciprocate with the same frequency but out of phase with one another, and said skirt and said sleeve bounding an annular space constituting a compressor cylinder which is vented to the crankcase and which, at given times, is opened -to said transfer passages'and, at other times, to said cylinder inlet.

In testimony whereof I have signedl my name to this specication.

JAMES WALTER ROBERTSON. 

